For next generation of mobile telecommunications systems the 3rd Generation Partnership Project (3GPP) is in the process of defining solutions for user equipment (UE) measurement logging function and immediate reporting function called Minimizing Drive Tests (MDT). The MDT study aims at assessing the feasibility, benefits and complexity of automating the collection of UE measurements to minimize the need of manual drive-tests. The work under the MDT study should define use cases and requirements for minimizing drive-tests in next generation LTE/HSPA (Long Term Evolution/High Speed Packet Access) networks. Also, based on the defined use cases and requirements, the MDT should focus on study the necessity of defining new UE measurements logging and reporting capabilities for minimizing drive tests and analyze the impact on the UE.
The use cases for the MDT will be given as following.                Radio coverage optimization        Mobility optimization        Network capacity optimization        Parameterization for common channels        Quality of Service verification        
The network can request the UE to perform logging of measurements. The UE executes measurements and logs these measurements internally in a sequential manner, containing e.g. some hour of logged measurement information.
When the UE has logged measurements the UE indicates to the network that it has an available measurement log. The network may then request the UE to deliver the measurement log. This prior art procedure is illustrated in FIG. 1. The UE sends 10 an indication to a network node, e.g. an eNodeB comprised in a LTE system or a RNC (Radio Network Controller) comprised in a WCDMA system, that it has an available measurement log. The network node then determines 11 whether is wants to request the measurement log. If it determines to request the measurement log it sends 12 a request to the UE. Thereupon the UE delivers 13 the measurement log to the network node. From the eNB/RNC, the received measurement log is sent to an OAM (Operation and Maintenance) or similar server (not shown) comprised in the network.
The network collects measurement logs from several UEs in different cells. By collecting and retrieving information from the measurement logs the network is able to perform optimization of radio coverage, mobility, network capacity and to perform parameterization for common channels and verification of QoS.
The current 3GPP assumptions on the measurement log feature are:                The UE is required to maintain only one measurement log at a time.        The measurement log only contains measurement information collected in one RAT (Radio Access Technology). The RAT being the type of radio technology used in a Radio Access Network (RAN) to access the Core Network (CN) in the wireless communication system, e.g., UMTS, GSM/EDGE, CDMA2000, WiMAX.        If the UE is requested to start logging measurements, a previously stored measurement log in the UE is erased.        
The current 3GPP assumption is that the MDT measurements are reported in the same RAT as they have been measured in. If the measurement log can only be reported in the RAT where the measurements are collected, a number of measurements can be lost or delayed for such a long time that they are not usable. The reasons why a UE may not stay in one and the same RAT are mainly related to network deployment and service provisioning. An existing operator's network is often a combination of two or three RATs and designed to work together in order to maximize the service offerings and geographical coverage area in a cost efficient way. This often means that there is not a uniform coverage of the different RATs (one RAT can have spotty coverage while the others are more globally available, e.g. because of propagation characteristics and/or service reasons). There are also various load balancing schemes used by an operator that also will make a UE move between RATs. The detailed measurements stored in the measurement log are typically RAT-specific. Consequently, the reporting of the measurements in another RAT than in which they were collected would not be understood. Moreover, it is neither possible to send the reported measurement log to another RAT to e.g. convey the information to the right place.
Another consequence of the current 3GPP assumption that the MDT measurements are reported in the same RAT as they have been measured in is, for the case where a UE has been logging measurements in one RAT, that these cannot be delivered in case the UE re-selects to another RAT. Furthermore, in case the UE is requested to perform logging of measurements in the new re-selected RAT, the measurement log stored while the UE was in the old RAT will be lost. Hence, resources are wasted.